Introduction to Terpenes
Introduction to Terpenes
probably the largest group of compounds, at least 25,000, many yet to be described
C5-C10-C15-C20-C25-C30-C40
terpenes are common in plants and fungi
they rarely accumulate in bacteria. Terpenes are also synthesized in (some) animals
Isoprene rule
Wallach
"biogenetic isoprene rule" Ruzicka
Where do the C5-units come from?
Mevalonic acid
This compound was thought to be the source of all terpenes from the 1950s until the 1990s.
This is the only pathway in animals, fungi, certain bacteria, archaea, and some protozoa.
Many bacteria, green algae, streptomycetes, mosses, liverworts, marine diatoms, and higher plants use this pathway to synthesize some terpenes and the DOXP pathway to synthesize others.
only the 3R-form used
mevalonic acid ----> IPP; IPP interconverts with DMAPP because of an isomerase
this pathway is associated with the cytoplasm
sterols ---> cytoplasm
DOXP Pathway
Hemiterpenes, usual monoterpenes, diterpenes, and tetraterpenes or carotenoids are usually from this pathway in plants.
chloroplasts appear to be autonomous in terpene production
carotenoids, sidechains of chlorophyll in chloroplasts
Hemiterpenes
mostly formed by adding DMAPP to molecules of various origins with prenyltransferases
in some cases these appear to be free radical reactions
both C and O alkylation
Chromenes, benzofurans and prococcenes
about 200 known, mostly from Asteraceae
These compounds have potent activity in some insects. Precoccenes cause precocious development of insects that are not entirely functional
precoccenes - cause changes of development in insects
corpus allatum, a vital gland in insects, but the compounds are highly specific as to which insects they affect ... this limits their use as insecticides
Encecalin is moderately toxic
"milk sickness" and tremetone
This is most commonly from Eupatorium rogosum, Asteraceae, white snake root, a very common plant in the midwestern U.S. This plant is one of the most common causes of livestock poisoning in the U.S. The toxic substances are excreted in milk. Similar compounds are found in an Isocoma species in the Southwestern U.S.
the plant compounds are not extremely toxic, but are activated in the liver to cause poisoning.
Polyterpenes
at least 2000 species contain polyterpenes.
latex - laticifers
latex contains nuclei, mitochondria, ER etc. as well as polyisoprene and resin particles
IPP in Hevea brasiliensis is incorporated into rubber about 97% yield
GPP or IPP addition onto a FPP starting unit
rubber elongation factor, a protein, published earlier is now considered as misinterpreted
rubber MW about 500,000
rubber doesn't turn over, probably not a food reserve
Natural rubber is allcis-1,4-polyisoprene/P>
Gutta percha
Gutta percha is all trans-1,4-polyisoprene. This material has special uses as well. It is often used to pack the inside of "root canals".
Chiclé
chiclé a 70:30 mix of 1,4-polyisoprenes. Used for chewing gum. From Manilkara sapota, Sapotaceae
Prenylation of proteins
still little known
Other 5 carbon units
not from mevalonate or DOXP
Formation of Major Groups of Terpenes
Stereochemistry of Mevalonic Acid Biosynthesis
Precocenes and Related Compounds
Non-Isoprenoid compounds with 5-Carbon Units
Plants with Hemiterpenes and
Polyterpenes
© David S. Seigler, Integrative Biology 425, Plant Secondary Metabolism, Department of Plant
Biology, 265 Morrill Hall, 505 S. Goodwin Ave., University of Illinois, Urbana, Illinois 61801, USA.
217-333-7577. seigler@life.uiuc.edu.
